From Pin to Pendant
Peggy's clutch purse idea on episode 8 of metalchik reminded me of these pin converters that I had seen:

They're available from Fire Mountain Gems (look in findings under bails, pin converters). If you would rather wear your vintage pin as a pendant slip the tube of the converter over the pin stem, run a chain through the bail or bead a matching necklace, and you're done.
Or you can make your own pin converter by wrapping a little wire around a mandrel a little bigger than the pin stem....

